1. Field of the Invention
The present invention relates to an image processing apparatus for electrically processing an original image.
2. Related Background Art
Image processing apparatuses such as facsimile systems are conventionally available which photoelectrically read original images and electrically process read image signals. In such an image processing apparatus, digital processing is more often performed recently due to the resulting simple processing and to its resistance against influence of external noise. Then, original images must be correctly converted into digital image signals.
Original images to be read have various states (density, size and the like), and they cannot all be processed by a single processing method. In view of this, the operator must first determine the type of an original image and adjust the image processing. However, such an adjustment is cumbersome and may result in an erroneous adjustment.
It can therefore be proposed to incorporate in an image processing apparatus a function for detecting the state of an original image and for automatically performing image processing suitable for each original image. With this method, the operator need not perform the adjustment described above, and an operator who is not accustomed to operation of image processing apparatuses in general can perform image processing with ease and accuracy.
However, when a reference signal for quantization of the image signal is determined in such automatic processing, the contents of an original image cannot be detected. That is, if the image density level is the same, original images of different contents may be quantized with the same reference signal. Thus, an image which must be emphasized, for example, cannot be properly emphasized.